is it possible that str and unicode str are treated differently, i.e.
unicode str does not give memory back? jonas borgström noticed the
following behaviour:

>>> resident_size()
3780
>>> a = ["%i" % i for i in xrange(2**22)]
>>> resident_size()
239580
>>> del a
>>> resident_size()

4128    <-- Most memory returned to the os
>>> a = [u"%i" % i for i in xrange(2**22)]
>>> resident_size()
434532
>>> del a
>>> resident_size()R

401760  <-- Almost nothing returned to the os 


for details see
http://groups.google.com/group/trac-dev/browse_thread/thread/9de74e1d2f62e2ed.

This is a duplicate of issue 2321. There was no memory leak whatsoever,
instead, malloc just failed to return the memory returned to it (through
free(3)) to the operating system. Don't trust resident_size() to detect
memory leaks; that approach is fairly flawed.